As you probably know, When you kill something with the "Slain enemies rest in pieces" legendary affix ( like Sever / Boneshatter / Last breath ) you get a huge crit damage hit this is useful if you have lifesteal. Here is another trick:
If you use the demon hunter ability Marked for Death - Grim Reaper on a mob and then someone ( does NOT have to be the demon hunter ) kills the mob with the legendary affix "Slain enemies rest in pieces" the huge crit will affect mobs around and most likely 1 shot them.
You can use it for example in MP10 ubers - barbarian with sever kills skeletons near the skeleton king while the skeletons are under the effect of Grim Reaper.
Have fun!